Grate construction



Dec. 28, 1943. F, H DAVIES 2,338,027

GRATE CONSTRUCTION File d Nov. 29, 1940 Patented Dec. 28, 1943 UNITED STATES enrsNr OFFICE GRATE CONSTRUCTION Frank H. Davies, Detroit, Mich. Application November 29, 1940, SerialNo. 367,839

11 Claims.

This invention relates to grates of the general type employed in connection with furnaces for the combustion of solid fuel, particularly to grates employed as fuel bed supports in mechanically fed fire boxes which, are provided with means for supplying combustion supporting air under pressure.

In furnaces of the mechanically fed forced draft type it is now customary to employ inclined grates of relatively large size, coal or other solid fuel being fed onto the grate at its upper end to form an inclined fuel bed and air for supporting combustion being blown into the fuel bed through apertures or interstices in the grate structure. It is also common practice to provide structures of this kind with control devices of various types to regulate the volume and velocity of air passing from the air supply means or wind trunk, to the grate, and. thereby to control the rate of combustion of the fuel resting upon the grate. While suflicing to regulate the entire amount of air flowing to the burning fuel, such means of the type heretofore utilized has not been so designed or constructed as to make it possible to control the rate of supply of combustion supporting air to any selected area or zone of the fuel bed. For this reason it has not up until this time been possible to prevent occasional local overheating of such grates and destruction of portions thereof by reason of such overheatmg.

Thus, despite such precautions as may -be taken to ensure even feeding of the fuel downwardly over the grate and to thus ensure that the depth of fuel upon all areas of the grate is the same, it sometimes happens that thin spots occur, a thin spotbeing a small area of the fuel bed in which the depth of fuel is considerably less than that overlying larger areas of. the bed. As the combustion supporting air will naturally tend to seek the path of least, resistance, a, greater volume of air will pass through a thin spot than through other areas of the grate; where the layer of superposed fuel is thicker. This in turn causes the fuel at a thin spot to be more rapidly consumed and a higher heat generated, the glowing fuel likewise more closely approaching the grate bars, the effect of all this being very frequently to overheat and severely injure that portion of the grate which underlies the thin spot. Sometimes the metal ofthe grate underlying such a thin spot is caused to be melted and in any event it is heavily distorted, in either case it being necessary to shut down the furnace in order that the injured units of the grate may be removed and replaced by new units.

A well-known type of grate is built up of what are generally designated tuyre blocks or fuel plates, a very considerable number of identical blocks or plates being assembled together, each plate having a fuel supporting surface and means defining an aperture for the passage of combustion supporting air. Where hot spots occur, it is possible to remove damaged tuyere blocks and substitute new ones, but of course it is costly to do this, not only from the standpoint of labor and material but also because of operating time which is lost.

In accordance with the present invention there is provided, in addition to devices, if any, which may be utilized to control the main streamef combustion supporting air on its Way to the grate, means for locally controlling the how of air through the grate at each area of the grate so that, whenever a local hot spot tends to form,

thus endangering a portion of the grate, the flow of air to that particular spot is reduced in volume, this in turn decreasing the rate of combustion of the fuel at that point and preventing over heating of the grate, all this being automatically effected without changing the rate or volume of flow of air to other areas of the grate, at least without actually decreasing the flow of combustion supporting air to such areas.

While the specific means for accomplishing this highly important object may be varied, I prefer, in the case of a grate embodying a plurality of tuyere blocks, to provide each tuyre block or fuel supporting plate with something in the nature of an automatically operating damper device which is responsive to changes in temperature of the fuel being consumed in the immediate vicinity of that tuyere block. Each tuyere block is so formed, as has previously been explained, that it includes not only a portion having a fuel supporting surface but also includes a portion,

which defines a passage for combustion supporting air, either a complete passage or a passage which it partially defines and which is completed by the next adjacent tuyere block. A popular type of tuyre block, for instance, is generally flat, having a substantially plane or flat side surface, a portion of which surface is adapted to be horizontally disposed and to face upwardly when the block is positioned in a grate to support a portion of a fuel bed, the opposite or undersurface of a block so positioned being, provided with a plurality of ribs extending axially of the block and defining, with a portion of the upper.

surface of the tuyre block next below, a series of passages through which air may pass from the space beneath the grate directly into the fuel bed.

The automatically operating air flow controlling or damping means which I utilize in association with each such plate may comprise a plurality of bi-rnetallic damper elements of known type, each such element being attached to the body of the tuyere block and being so designed and constructed that it will lie flat against the wall of the associated passage so long as the tuyere block to which it is attached does not become overheated, but which automatically defleets when the temperature of the tuyere block exceeds a predetermined maximum, swinging transversely of the air passage in which it is located and more or less blocking such passage so as to reduce the flow of air to the overheated spot and thus reduce the rate of combustion which, in turn, lowers the temperature and prevents injury to the grate.

The automatically acting damper means may be formed in various ways in adapting the invention to tuyre blocks of various types, as will be appreciated by one skilled in the art. By way of example two satisfactory types of damper construction will be hereinafter described but the invention naturally contemplates others of generally similar nature.

In the drawing:

Figure l is a side elevation of a tuyre block embodying the invention;

Figure 2 shows the same block in plan, as viewed from below, the automatically acting air flow control elements or dampers being clearly shown;

Figure 3 is a view similar to Figure 2, showing in bottom plan modified type of tuyere block embodying the lllVl "ion, the thermo-responsive dampers being show. in normal position in full lines and in passage blocking position in dotted lines;

Figure 4 is a vertical section through a portion of a grate built up of tuyere blocks of the type shown in Figures 1 and 2;

Figure 5 is a section on line 55 of Figure 2, the damper member illustrated being shown in its two extrem positions, by means of full and dotted lines; and

Figure 6 is a section on line (5-25 of Figure 3.

The tuyere block of Figures 1 and 2 is of wellknown type and its details need not be described except insofar they have bearing upon the present invention. The block in its entirety is preferably cast iron, formed as one integral member with generally flat upper surface, the forward portion of which, generally indicated at 26, is disposed substantially horizontally when the block is assembl d a grate structure, as shown in Figure 4, and is a fuel bed supporting surface. The node face of the tuyre block is provided with 2i and each pair of ribs defines, together with the body of the tuyere block above them, the upper surface of the tuyere block next below, a passage for combustion supporting air. Air is delivered to the grate in the direction indicated by the arrow A in Figure l, being divided by the tuyere blocks into a multitude of minor streams which enter the fuel bed at a great number of points, in well-known manner.

In each of the air passages thus defined is located a thermo-responsive air flow control memher or damper member being for instance a bi-metallic plate or blade of the type which will arch or curl in one direction with increase in temperature and in the opposite direction with decrease in temperature. One end of each blade is attached to the body of the tuyre block as by screws or rivets, screws being indicated at 23 in he drawing. Each damper element 22 is so constructed that it will lie normally in the position in which it is shown in full lines in Figure 5 for all ordinary operating conditions of the grate but, if a thin spot forms and the temperature above any closely associated group of tuycre blocks rises to a dangerous degree, the increased temperature of the tuyre block is communicated to the damper blade, which will cause the free end of the blade to move downwardly, for instance to the position in which it is shown in dotted lines in Figure 5, thus causing the blade to at least partially block the air channel in which it is located. This, of course, greatly reduces the flow of air through this particular channel, lowers the rate of combustion of the adjacent fuel and therefore lowers the temperature within a short time. When the temperature in the fuel bed decreases to such degree that damage to the tuyre block no longer threatens, the damper device will return to original position, or return part way, automatically seeking a position such that combustion may occur at a rate which is not dangerous to the grate but which is nevertheless as high as may take place with safety. Hence the rate of combustion of each area of the grate is locally controlled and excessive temperature at any one spot avoided, thus prolonging the useful life of the grate, and saving the large expense incident to shutdown and repair.

The ai conducting channels in each block may be varied as desired, within limits, and thermoresponsive damping devices designed accordingly. For instance, instead of utilizing a horizontally disposed bi-metallic blade of the type shown in Figure 2, a vertically disposed blade may be employed which curls or archs horizontally to close the duct in which it is located, blades of this type being shown in Figure 3. In this figure a plurality of arcuate ribs on the undersurface of a tuyere block are indicated at 25 and intermediate each pair of ribs 25 is a shorter arcuate rib 255. Passing around the forward end of each rib 28 is the curved mid-section of a bifurcated or U-shaped bi-metallic damping device 21, these devices or elements being relatively thin but as wide as the ribs are deep, as indicated in Figure 6, The damping elements may be attached in position by means of screws or other fastening devices, or by welding, and normally lie with their inner faces in close contact with the side surfaces of the ribs 26 to which they are fastened. Should the temperature of the tuyere block exceed a predetermined minimum, however, due to the formation of a thin spot in the fuel bed, the damping elements 2! will curl or arch, the free ends of these elements moving horizontally across the air conducting passages and thus reducing the flow of air to the extent necessary to effect starvation of the adjacent fire, decrease in the rate of combustion and lowering of the temperature. Naturally, other types of automatically operating local thermo-responsive damping means may be provided in association with tuyre blocks or grate structures which vary in detail from that shown.

A thermo-responsive damping means will in every instance be chosen which will give the tem perature control preferred. If the bi-metallic members employed operate to close the passages when the temperature of the associated tuyere blocks reaches approximately 1000 F. both blocks and bi-metallic members will be safeguarded and it is generally undesirable to permit higher temperatures. The air passages should open again when the temperature falls to between 600 F. and 800 F., which may easily be arranged, so that the tuyere block temperatures will remain always within the desired approximate upper and lower limits.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A grate comprising a plurality of tuyere blocks assembled together, each block having a fuel supporting surface and a passage for air, and a thermo-responsive damper device secured to each block for reducing the effective area of the air passage when the temperature of the block itself due to the combustion of the fuel immediately adjacent thereto exceeds a predetermined minimum.

2. A grate comprising a plurality of tu'yere blocks assembled together, each block having a fuel supporting surface and a passage for air, and a bi-metallic thermo-responsive damper blade secured to each block, said blade curving or arching across the air passage to reduce its effective area when the temperature of the block itself due to the combustion of the fuel immediately adjacent thereto exceeds a predetermined minimum.

3. The combination set forth in claim 2 in which the blade is attached at one end to the block and normally lies close to a surface of the air passage.

4.. The combination set forth in claim 2 in which the block has at least two adjacent air passages separated by a rib or partition and the bi-metallic blade is U-shaped, one arm thereof lying in each passage.

5. A tuyere block comprising a fuel supporting surface, an air passage, and a temperature responsive damper device secured to the block and positioned to control the flow of air through said passage.

6. A grate structure for supporting .a bed of solid fuel, said grate structure having a plurality of relatively small apertures therethrough so constructed and arranged as to deliver combustion air through the grate without permitting the passage of fuel, thermo-I'esponsive dampers for controlling each of said apertures in the rate to reduce its effective area whenever the temperature of the grate itself in the vicinity of the aperture exceeds a predetermined amount, said dampers being disposed in heat conductive relation to the grate adjacent said apertures.

'7. A gate structure for supporting a bed of solid fuel, said grate structure having a plurality of relatively smal1 apertures therethrough so constructed and arranged as to deliver combustion air through the grate without permitting the passage of fuel, bi-metallic thermo-responsive damper blades for controlling each of said apertures in the grate to reduce its effective area whenever the temperature of the grate itself in the immediate vicinity of the aperture exceeds a predetermined amount, said dampers being normally disposed in heat conductive contacting relation to the grate adjacent its combustion surface.

8. A self-adjusting grate construction for furnaces or the like adapted to prevent local overheating of the grate due to uneven combustion of the fuel thereon, said grate being provided wit a plurality of apertures for the passage of combustion supporting air, the grate including a thermo-responsive means attached thereto adjacent each of said apertures, which means is responsive to temperature changes in the grate structure in its immediate vicinity and adapted, by thermal expansion as a result of an increase in such loca1 temperature, to at least partially close the aperture with which it is associated.

9. A self-adjusting grate construction for furnaces or the like adapted to prevent local overheating of the grate due to uneven combustion of the fuel thereon, said grate being of metallic construction and provided with a plurality of apertures for the passage of combustion supporting air, a unitary portion of the grate adja cent each of said apertures being of bi-metallic construction responsive by heat conduction to temperatures of the grate structure in its immediate vicinity and adapted, by differential thermal expansion to warp, as a result of an increase in such local temperature, to at least partially close the aperture with which it is associated.

10. A tuyere block for use in furnace grates or the like comp-rising, in combination, a substan tially horizontal fuel supporting surface and a plurality of longitudinal ribs on its undersurface adapted to cooperate with the upper surface of a subjacent block to provide transverse passageways through the grate, and thermo-responsive' dampers disposed between said ribs and adapted to control the flow of air through said passageways.

11. A tuyere block for use in furnace grates or the like comprising, in combination, a substantially horizontal fuel supporting surface and a plurality of longitudinal ribs on its undersurface adapted to cooperate with the upper surface of a subjacent block to provide transverse passageways through the grate, and a plurality of thermo-responsive dampers secured to said block in heat conducting relation thereto between said ribs and adapted to warp to and from a position transversely of said passageways to control the flow of air therethrough.

FRANK H. DAVIES. 

